The present disclosure relates generally to techniques for performing wellsite operations. More specifically, the present disclosure relates to techniques, such as blowout preventers (BOPs), packers, and/or ram blocks, for sealing wellbores.
Oilfield operations may be performed to locate and gather valuable downhole fluids. Oil rigs are positioned at wellsites and downhole tools, such as drilling tools, are deployed into the ground to reach subsurface reservoirs. Once the downhole tools form a wellbore to reach a desired reservoir, casings may be cemented into place within the wellbore, and the wellbore completed to initiate production of fluids from the reservoir. Tubing or pipes may be positioned in the wellbore to enable the passage of subsurface fluids to the surface.
Leakage of subsurface fluids may pose a significant environmental threat if released from the wellbore. Equipment, such as blow out preventers (BOPs), may be positioned about the wellbore to form a seal about pipes therein to prevent leakage of fluid as it is brought to the surface. In some cases, the BOPs employ rams and/or ram blocks that seal the wellbore. Some examples of BOPs and/or ram blocks are provided in U.S. Pat. Nos. 4,647,002, 6,173,770, 5,025,708, 7,051,989, 5,575,452, 6,374,925, 2008/0265188, 5,735,502, 5,897,094, 7,234,530, 8,544,538, 8,136,247, 2010/0243926, and 2012/0012340. The location of the ram and/or ram block of a BOP may be measured by visually looking at a tail shaft of the ram blocks. Ram position sensors may be provided as described, for example, in US Patent/Application No. 2008/0197306, U.S. Pat. Nos. 4,922,423, 5,320,325, 5,407,172, and 7,274,989.